Method of making a butt joint by explosive welding



Jan. 23, 1968 E. L. ARMSTRONG 3,36

METHOD OF MAKING A BUTT JOINT BY EXPLOSIVE WELDING Original Filed Nov.8, 1962 EXPLOSIVE mun 43 EXPLOSIVE E JET -=1 INVENTOR. mm

FIG EDWARD L. ARMSTRONG ATTORNEY United States Patent 1 Claim. (Cl.29-47(11) This is a division of application Ser. No. 236,211, filed Nov.8, 1962, now abandoned.

This invention pertains to a novel method of welding. More particularly,the invention pertains to a novel method of welding utilizing explosiveenergy.

The herein invention utilizes the high pressure realized from thedetonation of an explosive to cold weld similar or dissimilar metals.The steps that will be set forth can relate to short or long lap jointsor can be utilized in the particular area of welding or bonding tubes tothe usual tube sheet utilized in tube and sheet heat exchangers.Additionally, there is no successful means previously known for weldingrefractory materials and many of the high temperature metals. Theapparatus that is available for welding or bonding unusual materials isnormally of a very complex nature and is quite large, cumbersome andbulky. As an result, this type of equipment is not feasible forutilization in welding applications in outer space where Weight and sizeconsiderations become a factor of great importance.

An object of this invention is to describe a new method for cold weldingof similar or dissimilar metals.

An additional object of this invention is to provide a method forwelding of materials normally not joinable by conventional weldingtechniques, such materials including refractory materials and hightemperature metals and alloys.

Another object of this invention is to provide a simple, compact methodfor cold welding of metals for use in outer space applications.

A still further object of this invention is to provide for a continuousmetallurgical bond in sealing tubes to the tube sheet of a heatexchanger.

Other objects and attendant advantages of the present invention willbecome more apparent from the detailed drawings.

The invention herein described consists of providing one of the twosurfaces to be joined by the application of explosive force with asurface having a multitude of angles relative to the other sheet ormaterial to which it is joined. The multi-angular surfaced material maybe'prepared by providing a plurality of V-shaped grooves, broad shallowgrooves, a multitude of tapers, surface moldings or the like in varioustypes of geometrical configurations so as to provide the desired angularsurface. In joining the two workpieces, the angular surfaced one isplaced in relatively close proximity or abutting relationship to anotherplanesurfaced workpiece forming included angles therewith. An explosivecharge is detonated so as to cause the materials to be joined. Theexplosive utilized is chosen to produce an explosive force sufiicient todrive the pieces together creating the desired bonding. The same elfectmay alternatively be accomplished by providing both of the abuttingsurfaces to be joined with complementary angular sur-.

faces, such that a net result similar to that described with relation toone angular surface alone is obtained. It is believed the invention willbe better understood with relation to the following detailed drawingsand descriptions in which:

FIG. 1 is an illustration of two flat surfaces to be joined having anexplosive force applied to one side of the two flat surfaces andillustrating a jet formation.

FIG. 1a is a cross-sectional view of a piece subjected to an explosivejet.

FIG. 2 is a cross-sectional view of a tube and sheet having a variety ofangular configurations provided on the tube.

FIG. 3 is a cross-sectional view of a tube to be joined to a tube sheetindicating the relative placement of the explosive charge utilized inaccordance with this invention.

FIG. 4 is an additional embodiment of the invention.

FIG. 4a is the finished piece of that shown in FIG. 4.

The collision of solid bodies moving at high speeds produces largepressure shock waves, large strains and in certain instances instabilitywhich may result in a breakup of surfaces and formation of high velocityfluid-like jets. As seen in FIG. 1 when two slabs of metal are inabutting relationship at the left of the two pieces and force is appliedto either one or both of the two members so as to cause them to bebrought together, a shock wave is formed by the force of the rapidmovement of air between the two pieces. This shock wave is commonlyreferred to as a jet. The jet is the result of a rapidly-formed highpressure region between the two pieces due to their relative movementone to the other. Attendant with this rapid increase of the pressurebetween the two pieces is a rapid increase in temperature such that thesurface of the metal is melted or the adjoining metals go into solidsolution. In FIG. 1a showing a cross section of a piece so-exposed tojet action, a plurality of wave-like motions is found on the surface ofthe member subjected to the jet. These waves are a result of the shockwave passing over the surface of the metal as it is brought togetherwith the opposite piece. The phenomenon recited with relation to thecreation of a jet between adjoining metal members particularly lendsitself to the field of explosive energy where great and rapid forces canbe exerted upon surfaces desired to be formed. It is the utilization ofthis jet principle that forms the basis for the invention as willhereinafter be explained.

In welding or bonding materials utilizing the jet force, it isimportantto note that the welding is dependent on the force supplied, type ofmaterial utilized, the jet angle and distance between the two materialsbeing formed. With the type of relationship between the two pieces asshown in FIG. 1, it is to be pointed out that beyond the first one ortwo inches from the hinged portion or abutting portion, the two partsare physically too far separated to be welded. Beyond the aforesaidfirst one or two inches the effect of the jet is substantiallydissipatedand virtually no surface melting would occur.

As seen in FIG. 2 and as will be described, the invention provides amethod of welding or bonding material utilizing the jet efiect such thatlarge sheets or cylindn'cal sections such as in a tube and sheet heatexchanger may be welded. In FIG. 2, a tube sheet 11 is prepared toreceive the tube member 12 within the opening 13 which has a diameterslightly larger than that of the tube. By way of illustration the tubemember 12 is shown as being provided with a plurality of different typesof angular configurations upon the outer circumference thereof so as toutilize the effects of the inventive concept as disclosed. Any one ofthe configurations shown would suffice for effecting the desired bondingof the tube to the tube sheet. Alternatively, these configurations maybe cut into a flat surface when it is desired to bond it to anothersurface of that type. For example, the tube may be prepared with aplurality of successive small tapers 14 about the circumference. Aknurled preparation 15 on the tube also effects the desired end result.As is indicated, circumferential V-shaped grooves 16 around the tube,shallow, broad grooves 17 and the sawtooth-shape circumferential grooves18 additionally provide a desired angular outer surface on the tube tobe bonded. Furthermore, additional ways of preparing the tube includeslightly tapering as at 21 the tube sheet adjacent the end thereof. Whenextending the concept to flat sheets, corrugated sheet members may beutilized to effectively encompass the concept of the invention. Itshould be established that the particular geometrical configurationsshown and discussed are by way of example only and that virtually anysurface preparation that permits a plurality of multi-angular surfaceswill generally suffice for the purposes of explosive bonding as taughtin this invention. As previously indicated, the tube sheet holes may beprovided with such multi-angular surfaces rather than the tubesutilized.

When detonating an explosive charge within the tube as will hereinafterbe explained, a jet is produced at each of the many angles presented bythe structural configuration of the two pieces to be joined. Forexample, at each V-groove or knurl or sawtooth and the like a small jetis formed upon the detonation of the explosive utilized. This jet, aspreviously discussed, serves to slightly melt the surfaces of the twomaterials being joined permitting a fusion upon their contact or causethe two materials to go into solid solution giving a metallurgical bondwithout fusion. It is apparent that this feature of the invention reliesupon a plurality of small included angles between the pieces beingjoined such that there is virtually no dissipation of the effect of thejet created between such included angles. As can be seen, a successiveseries of small jets is effected by the invention to produce the desiredend result.

Example FIG. 3 represents the positioning of the explosive and tubeprior to the joining operation. Tube 31 is provided with concentrictapers 32 by a machining operation. The tube 31 was 304 stainless steel,one-half inch IPS schedule 40. The tapers were three-quarters of an inchlong and had a 2 inclination. Prior to the tube insertion in the tubesheet to which it is to be bonded, the tube and sheet were cleaned withacetone. The explosive charge 33 is first inserted into either a Tygontubing or black rubber hose 34 which serves as the shock transportmedia. Other material may be used which will suffice for transportingthe shock than specifically enumerated, however. Specifically, othertransfer mediums such as water, plastics and the like are applicable.The explosive charge which is encased by the transport medium is theninserted into the tube to be bonded. The tube may be made typically outof 304 stainless steel. A flat, hard rubber disc 35 is placed over andadhesively bonded to the exposed base of the tube sheet 11 to protect itfrom marring by the resultant explosive fragments. Finally, a detonationcap 36 having leads to a detonator is attached and the charge isdetonated.

Upon inspection, a successful bonding of the tube to the tube sheet wasobtained. The bonded area varied from continuous fusion to intermittentfusion to metallurgical bonding without fusion. This result is probablydue to a process variable such as shock wave geometry. The specimen washelium-weight checked before and after six thermo cycles between roomtemperature and 1300 F. Three of the thermo cycles were followed by aircooling to room temperature while the other three were followed by awater quench to room temperature. The bond between the tube and the tubesheet was impermeable to helium before and after this severe treatment.The explosive charge utilized was pentaerythritol tetranitrate having400 grains per foot. This explosive has approximately a detonation rateof 7000 meters per second. It should be understood that there is greatvariance as to size, shape and exact detonation rate of explosivedepending upon the application and the geometry for which it is used.Generally, the explosives used, transfer mediums applicable, and variousparameters relating thereto are well known in the art of explosiveforming and can readily be applied to the concepts of this invention.

A further aspect of this invention is illustrated in FIG. 4 where amethod for providing for cold welding long lap joints of similar anddissimilar metals can be obtained utilizing the principle of thisinvention. The metal sheets 41 and 42 to be welded are ground to apreferred angle of 10 to 50 depending on the width of the overlapdesired, thus, providing adjoining beveled surfaces 43 and 44,respectively. The sheets 41 and 42 are positioned in a welding jig andare slightly overlapped whereby the beveled side of the one sheet 42 isin contact with the plane unbeveled surface of the opposite sheet 41.Propagation material such as rubber of proper thickness to provideoptimum stand-off distance is placed over the weld area with a sheetexplosive placed on top and taped in place. Upon detonation of theexplosive directly down upon the upper sheet 41, a jet is createdbetween the two sheets at the beveled area 44 of sheet 42.

In addition to a metallugical bond, the weld is planished by theexplosive force. As can be seen in FIG. 4a, a fiat bonded surfaceresults with the beveled edge 43 of sheet 41 being compressed at thebond area. Only mechanical cleaning followed by a degreasing rinse, suchas acetone, is used. Some materials such as aluminum generally require amore-extensive chemical cleaning cycle. The welding jig 46 utilized forthis type of application, though not part of the invention, iscomprised, as seen in FIG. 4, of a back up plate 47 and two hold downbars 43. The jig is made of hardened, high impact, shock resistant toolsteels. The jig 47 may be greased so as to prevent welding of the parts41 and 42 thereto. The top of the bottom plate and bottom surfaces ofthe hold down bars are ground to provide smooth appearance to the area.The hold down bars may be bolted, clamped as shown or held in place byhydraulic rams or other suitable means. The hold down bars are chamferedoutward from the bottom to concentrate the explosive force in the weldarea. If the material to be welded is such that it must be heated aboutthe transition temperature, then provisions may be incorporated withinthe jig for heating such as with resistance heating units.

As indicated, the process disclosed herein may be utilized for thebonding of similar and dissimilar metals. The application of theinventive concept is not limited to any particular known metal orvariations of metals to be bonded to each other.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaim.

I claim:

1. The method of explosively welding in a lap joint the edges of twometal sheets comprising:

providing a first metal sheet having top and bottom surfaces,

beveling an edge of said first sheet at an oblique angle extending fromsaid bottom surface to said top surface,

providing a second metal sheet having top and bottom surfaces,

beveling an edge of said second sheet at the same oblique angle as saidfirst sheet, said bevel extending from said bottom surface to said topsurface,

positioning said second sheet and said first sheet such that the bottomof said beveled edge of second sheet corresponds with the top of saidbeveled edge of said first sheet, effecting an overlap of said sheetsessentially equivalent to the width of said bevels,

placing an explosive charge adjacent said sheets,

exploding said charge so as to force said sheets into 10 a single planeefiecting a bond at said overlap area.

References Cited UNITED STATES PATENTS Armacost 29-482 Carter et a129--497.5 X Burman et a1. 29470.1 Maher et al. 29-421 Wright et a1.29-421 X JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner,

1. THE METHOD OF EXPLOSIVELY WELDING IN A LAP JOINT THE EDGES OF TWOMETAL SHEETS COMPRISING: PROVIDING A FIRST METAL SHEET HAVING TOP ANDBOTTOM SURFACES, BEVELING AN EDGE OF SAID FIRST SHEET AT AN OBLIQUEANGLE EXTENDING FROM SAID BOTTOM SURFACE TO SAID TOP SURFACE, PROVIDINGA SECOND METAL SHEET HAVING TOP AND BOTTOM SURFACES, BEVELING AN EDGE OFSAID SECOND SHEET AT THE SAME OBLIQUE ANGLE AS SAID FIRST SHEET, SAIDBEVEL EXTENDING FROM SAID BOTTOM SURFACE TO SAID TOP SURFACE POSITIONINGSAID SECOND SHEET AND SAID FIRST SHEET SUCH THAT THE BOTTOM OF SAIDBEVELED EDGE OF SECOND SHEET CORRESPONDS WITH THE TOP OF SAID BEVELEDEDGE OF SAID FIRST SHEET, EFFECTING AN OVERLAP OF SAID SHEETSESSENTIALLY EQUIVALENT TO THE WIDTH OF SAID BEVELS, PLACING AN EXPLOSIVECHARGE ADJACENT SAID SHEETS, EXPLODING SAID CHARGE SO AS TO FORCE SAIDSHEETS INTO A SINGLE PLANE EFFECTING A BOND AT SAID OVERLAP AREA.